Sticking It To the Grunts; Being in the infantry means you are most likely to get hurt, will have the worst living conditions and, to make a bad situation even worse, get the least attention when it comes to new equipment. It's not that armies don't try to equip their infantry well, it's just that these efforts so often fail. And such failure is often fatal for the ground pounders.

Idiotic equipment is less likely to be developed during wartime, but even then you get some real beauts. Consider, for example, where the steel helmet came from. Shortly after World War I began, everyone began to notice a very high proportion of head wounds. World War I was the first war that used a lot of artillery, which put a lot of metal fragments in the air, and any soldiers in the vicinity. Up until then, soldiers didn't wear metal helmets, because bullets or large, non-exploding shells, were the most common objects running into the infantry. A helmet was not practical. But with all the new shells, and their smaller, more numerous fragments, a steel helmet loomed as a cheap way to prevent a lot of injuries. So Britain, France and Germany proceeded, each in their own way, to develop some protection for their infantry. The French, being fashion minded, consulted experts in medieval armor and came up with a tasteful, elegant helmet that would not have been out of place in the 15th century. Unfortunately, it was now the 20th century and many needless French casualties resulted. The British formed a committee. They came up with a flat (literally) helmet that was vastly interior to the German helmet, which looked a coal bucket but provided the best protection. The Germans went and looked at what parts of the head needed the most protection and created a design that was eventually adopted by most of the world's nations (including the US, whose version is called "the Fritz".)

While the Germans do manage to lose wars, they also have a knack for taking better care of their infantry. Consider the idea of giving the infantry automatic weapons (what we now call "assault rifles.") The Germans were the first to do this, noting that machine-guns were the most lethal weapon the grunts had. So before World War I ended, some 18,000 MP-18 "submachineguns" (assault rifles firing 9mm pistol ammunition) were issued. By the time World War II rolled around, the Germans had a lot more submachineguns, but most of the infantry were still equipped with bolt-action rifles. The Russians, however, gave their troops a lot more submachineguns, and the Germans noticed the impact of entire units of submachinegun armed Russians attacking or defending. By 1943, the Germans were producing the StG (SturmGewehr, or Assault Rifle) 44 and tested it on the Russian front that year. The extensive reports of these tests, captured by US troops at the end of the war, made dramatic reading. The StG 44 was basically the same design as the later Russian AK-47. The StG 44 used a "short" rifle cartridge instead of the pistol round used by submachineguns. This game the StG 44 more range, hitting power and accuracy. The troops loved it. The Germans made as many as they could through the rest of the war. But only the Russians developed their own assault rifle right after the war; the AK-47. Everyone else felt the infantry did just fine with a semiautomatic (one shot at a time) rifle. 

Eventually, in the 1960s and later, the US, and most other nations, developed their own assault rifles (the M-16 and clones.) Why the delay? Simple, the generals didn't trust the troops to watch their ammunition supply and were obsessed with long range rifle fire (that required the larger cartridge.) It was an old problem. The same thing happened during the American Civil War, when the brass resisted adopting repeating rifles.
And just in case you think the brass have finally got the message, keep in mind that the U.S. M-16 was modified after the Vietnam war to fire three round bursts instead of full automatic. The troops would really, really like to get full automatic again. But, hey, that might waste ammunition.

The list of lost opportunities goes on and on. Take something as simple as the backpacks ("web gear" in milspeak) the grunts use to haul around all their gear. Since World War II, the army has made several attempts to, well, catch up with the outfits that make gear for civilians who like to hike and camp out. Again, the troops would often buy the better civilian gear with their own money. This became common during Vietnam, when there was a big civilian market for hiking and, since there was a war going on, officers were less likely to stop the troops from equipping themselves with better web gear and boots. The U.S. army is still trying to get decent web gear to the troops. 

In peace time, anyone can be an expert on what the infantry needs, especially if you are a general. So the troops get high tech portable anti-aircraft missiles (the Stinger), despite the fact that the US Air Force has kept enemy warplanes away from our infantry for over half a century. What they really want is a decent portable rocket that will blast a bunker or enemy troops barricaded inside a building. In practice, the troops often use anti-tank missiles for that, but, gee, it would be real nice is something cheaper (so you could have more of them) and more effective was available. And let us not forget some of the pathetic missiles the troops have been stuck with. The Dragon anti-tank missile, in service for some twenty years, was widely considered the first item to be "lost" when a shooting war came. 
If only the infantry were able to go into combat without some of this looser equipment in the first place.