“Taking paint off is as equally important as putting it on … the key is to minimize concern over any wastage that may occur … it is essential you give yourself permission to scrape off paint when it’s required, which is surprisingly often throughout a painting’s progress. What is revealed underneath can be very exciting … what is left underneath is the equivalent of a new ‘brushstroke’.”Gareth Edwards, “Painting Abstract Landscapes“, page 24
Oil paint, being so slow drying, gives you plenty of time to scrape off paint with a painting knife. If you mix together what you scrape off it’ll head towards a greyish ‘nothing’ colour, which has its uses and counters the feeling of wasting paint. I keep it in a corner of my palette as it can be useful for clouds, mixed with lots of white, as interesting greys.
With acrylics, if it’s recently dried, try being
aggressive assertive with a damp cloth or a wet wipe, maybe reaching for some hand sanitizer (alcohol) which will ‘encourage’ acrylic to lift. If there’s lot of dried texture, reach for sand paper.
With watercolour, a damp cloth or wet, stiff brush will lift a lot, but you could also spray the whole painting with water and then dab up and down with paper towel. Or with a “take that you uncooperative painting” put the whole painting under a tap or in a basin of water.
Never forget, it’s your time and materials to use as you choose. If you’re having fun, it’s not wasted. If you’re learning and/or exploring, it’s not wasted. If you’re painting, it’s not wasted, regardless of the outcome.