The most likely reason is because you are entering the market whilst price is currently going the way you expecting. This is a kind of “chasing the market” situation. But prices ebb and flow continually and if you buy on a rise, for example, then the price is soon going to drop back bit. I suspect you are looking at this on a macro basis from a very short time frame?
No one can, or expects to, buy or sell at precisely the top or bottom and it is a factor in any trade decision to decide how far one is prepared to allow the price to penetrate into negative territory before accepting it is wrong and closing it to protect capital. This may be a physical stop order or just a mental identification.
These fluctuations are much more magnified when trading short term positions, but if you are trading on a longer term basis then a pull-back of, say, 10-20 pips is of little significance compared with a target of maybe 200 pips or more.
Another factor is that your new position will always show a minus when it is executed to reflect the spread between bid/offer.