This is YouTube, a video streaming owned by one of the biggest companies in the world, Google.
At first, you may not see anything wrong, but there is a big mistake, they did poorly in one of the most important design principles, contrast.
I lost the count of how many times I was browsing for new videos of that channel, and I ended up watching repeated videos. It is very frustrating when you spend 30 seconds watching a video to then realize that you have already watched it.
The colour of the progress bar is almost the same as the thumbnail background, mistakes like this create frustrating experiences for users. YouTube could fix this simply by adding borders to the progress bar or changing the progress bar colour when the thumbnail has a similar colour.
This is just a small example of how UX design can impact you and how hard it is to actually to offer an awesome flaw-free experience to users.