Sorry, I couldn't resist.
If your stitch count stays constant, then it's hard to say. If you find that you have more stitches than you started with, you're probably doing an accidental yarn-over increase, which is supposed to leave a hole (eyelet). It happens when the yarn is in the wrong position when you knit or purl a stitch.
If the stitch count is correct, it might be possible to see what's happened by looking at it.
Occasionally, new knitters will pick up the work and start working in the wrong direction--that leaves a hole. In other words, let's say you've been working on a knit row, put it down and then pick it up and start purling back the other way by mistake. A hole occurs at that point. Just an example.