Quote Originally Posted by Lonnie
Losing creates self doubt. The luck factor in poker makes it very difficult to ascertain whether you are playing badly or the cards are just running cold.
One more point...

This is what Poker Tracker is great for. It can point out or eliminate a lot of areas as possible leaks. Although there are a lot of queries I wish it had...

Profit/Loss when facing a turn raise
Folded best hand post-flop
Missed river bets
# of sets vs expectation for a given pocket pair
...

Great places to start looking:
Cold calls
Suited connectors
Small suited Aces
Other specific hand play
Overall PFR + VP$IP compared to opposition and other good players with a similar approach.
Count sets vs expectation on losing pocket pairs
"Steal" situation performance
EV in the blinds. Most good players total around -0.25BB or less.