hey miro- i watch many of your videos and i think you are doing great work.  that said, i think the thumbnail for this one is not very good.  it's super hard to read the type against the background and in a grid of thumbnails it doesn't stand out.  try a simpler version, maybe fewer words or give the type an outline so its easier to read.  btw- youtube lets you a/b test thumbnails so it's a good idea to make a few different ones and let youtube show you which ones people are responding to.  appreciate you sharing your work with us, keep it up.