What was the time control? I know my question may sound silly but one of my opponents didn`t realize we were playing a 2/1 game and thought I was doing something with my time/clock. 
opponent gains time and wins
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I only play 5 minutes blitz.
What most likely happened was that lag made it seem like he was moving slower than he actually was. If he was using pre-moves then the amount of time he takes to move would be almost none thus letting him have 4 seconds of time left at the end.
I lost some games, because of time.
I had e.g. 10 seconds and my opponent 4 seconds, but something unbelevable happened. For each move my opponent gained half a second. This happenend for 10 moves and then I ran out of time. My opponent still had 4 seconds left!
It's not possible to play blitz under these circumstances!
What do you think?
Any help?