Up 4-0 and all of a sudden 4 goals scored by the opponent to win!

Happens all the time, that's why I don't usually quit if I'm 3-0 down at half time. I've been 5-0 up at half time, opponent not had a sniff at goal and I still manage to lose the game in the second half. I've also seen myself 3-0 down can't get out of my own half and in the second half I end up finishing with a win and with more shots on target than my opponent