The important things are always simple. The simple things are always hard. No-combat ready group has passed inspection. Things that must be together to work, usually can't be shipped together. Radios will fail as soon as you need fire support desperately.
Tracers work both ways.
The only thing more accurate than incoming enemy fire is incoming friendly fire. If you take more than your share of objectives, you will have more than your fair share to take. When both sides are convinced they are about to lose, they're both right. The enemy never monitors your radio traffic until you broadcast on an unsecure channel. Whenever you drop your equipment in a fire-fight, your ammo and grenades always fall the farthest away, and your canteen always lands at your feet.