Maybe try finishing some shorter games first. Before and after I take on a 20+ hour game, I like to mix in some shorter games. I find that just finishing a new game feels rewarding. Which usually gives me enough confidence and motivation to move on to the next game. I think of a short game like a movie. Whether or not a movie is good, at least you only lost around 2 hours. Anyway, that's just my 2 cents. L&R.
Some good short games from 2019: Arise A Simple Story, Telling Lies, Sticks and Bones, Sayonara Wild Hearts, Pilgrims, Ape Out.
All-time greats: Inside, Limbo, What Remains of Edith Finch, Braid, Hotline Miami, Gone Home, Her Story, The Stanley Parable, Abzu, Brothers: A Tale of Two Sons.