You definitely have to take breaks if silly mistakes are being made. My group has had T7 on farm for a long time and one night I just wasn't quite as focused as normal and kept voicing people as the main tank. It was very frustrating to say the least. After a small break, I came back with a renewed focus and we beat it.

Last night on our first T9 win, we were going at it hard and making it to divebombs consistently, then we started regressing, dying even before the golems came out due to a ill-placed meteor. We took a 10 minute break, came back and beat it.

Sometimes you just need to take a step break and refresh yourself and then go back at it.