There are no straight lines in life. Well. Not from my perspective anyways, if that counts for anything.
When we chart our own progress with anything; it's helpful to take a top down view. We tend to see things linearly if we don't and any set back or regression (which is normal) might be seen as a failing or a move backwards; and we feel disheartened. BUT, it's entirely normal for growth to be more of a wiggly trendline. It's just that we notice the dips more than the tops because we're designed to sense something threatening and focus our attention on that; such as a regression being threatening to our integrity/ego.
So next time you're feeling bummed about your apparent lack of progress, just look back and see how far you've come. Recognise that life is not a straight line. There are always ups and downs. Zooming out, take a birds eye view of your progress. It helps us get away from selective bias in our thinking.