I used to force myself to play only one at a time, in order to encourage to complete them more quickly so I can play the next one.
when I was playing too many at once I ended never completing any.
it worked fine for few years, but in 2017 I played only ONE game for 12 months ! (zelda botw) and I still haven't completed it.
I decided to drop playing only one game at a time because I missed the occasion to play lot of short games (10-20h) while still playing zelda.
I miss so much time to play, I can't focus on single game anymore. (I'm not even at 200H at zelda, after 1.5 years of playing it)
Now, I try to play only one "story game" at a time, but I play more at once, like racing or snowboarding, puzzle, etc.
I'm playing ni no kuni (only at 20h after 3 months), Steep, wipeout omega, just tried the witness this month.