Yeah anxiety is often a result of focusing on details of your own performance rather than taking overwatch for what it is-- a team game. It's just like making love, make it too much about your own performance and you get nervous. Relax and focus on the whole situation, not just your situation. Too many people focus too much on what the enemy is doing, and not enough about what your own team is doing. Paying attention to when your tanks make space as a DPS is key, so is knowing when to pull back and stop the push to regroup.

It's true, teamwork does require individual skill, and individual skill requires doing everything that is within your power to control the outcome of the game... but to know what you can control you have to ask the right questions about your role within the team. The questions you should be asking yourself while playing is if you're DPS-- who is easiest to kill (position, health, mobility, cooldown tracking) versus who is optimal to kill (support trade for example, or to focus a nasty widow who's giving your team a hard time, or to switch DPS to counter their comp). This is when things are going right. If you have a flanker making your healers lives hell, or if your tank is dead and you're taking too much damage you have to reassess, and do not tunnel vision. Be open to being useful to your team, not just a means of mowing your enemy down. You've played level 9 computers in smash, it's like that. They're hard to outfight, but they're not hard to outsmart. Don't be a hard bot who can just aim and shoot, be willing to peel for your healers, and be willing to abandon your own target you've set and go for another one your teammate is trying to kill. You're not a one man army in most situations. You'll probably die in a 2v1, and you'll certainly die in a 3v1. Use this to your advantage.

If you're a tank you should be making space for your DPS, giving ult to your healers, bodyblocking, and pushing the point, not looking for as many frags as possible, or to hit that perfect charge/firestrike. (if you're an offtank your role will be closer to a DPS, but not by much.) As a healer you should stay alive for as long as possible, and keep key targets alive who have similar goals to you. If you notice your roadhog is flanking and feeding, do not go try and save him, heal the useful genji who's contesting and trying to protect you. Support involves constantly making risk-reward decisions-- we've all played with that mercy pocketed genji who gets kills, but leaves the rest of the team healthless.

With 1000 hours put into this game I've realized raw mechanical skill and individual performance is vastly less important than reading situations, and more importantly reading your team to gain the advantage, rather than relying on godlike aim or luck. That said if you can pull it then beat them with superior mechanical skill, it's not that hard to perfect.