jsmith,
Your previous trade(s) should have no effect on your next trade. If you had a losing trade or a winning trade, you should not hesitate to take a another shot if your strategy presents you another opportunity in the market.
Shoulda, woulda, coulda. While I agree with you in theory, in the real world pretty much everyone is affected by previous trades, even as they know they shouldn't be. Especially if they are losing trades, even moreso if they are a series of losing trades. I'm sure those robots are out there, but I haven't personally met anyone who isn't seriously rattled by a long string of (mostly) losing trades.
You must believe in...your strategy completely.
Again, while I agree in theory, unless your strategy has proved consistent over a long period of time and a wide variety of market conditions -- and even then sometimes if it has -- an extended string of losing trades will put the fear of God in just about anyone. Hmmm, is it me, is it my strategy, is it the combination, maybe it doesn't fit me as perfectly as I thought, it seems like I'm doing things the same, maybe something's different, maybe something new happened in the market, is my concentration just slipping...
Theory is nice and makes for good conversation (especially with lots of shoulds thrown in), but real world psychology must be addressed and not ignored.