Picasso was a prolific artist. He changed his visual vocabularies (styles) many times. An art prodigy.
When Picasso began painting, he created excellent realist works.
There are many, many examples. Here is a very large work, Science and Charity, which is very classic and beautifully painted.
However, it is imperative that an artist - any artist - develop a distinctive style of his own that is appropriate for, and reflective of the time in which he works. So Picasso went on from classic realism to play around with several other styles. There was a Blue Period, (which people still adore today). During this phase, he was still working essentially realistically, although his subjects and backgrounds had become somewhat more stylized, as you can see , from The Tragedy, an example of the period.
Picasso painted this at fifteen years old. Let me say that again. FIFTEEN YEARS OLD. The amount of mastery you’d have to accomplish to paint at this level is, suffice to say, pretty insane. Structure, form, human anatomy, shape, proportion, line proportion, texture, and so much more you’d have to get right.
Although he was capable of making realistic paintings, he chose the way of abstraction, which I think made him an art genius.
One example is this series of bull images. It shows how he moved from very realistic to highly abstracted painting. You could easily tell that the most abstract image is clearly a bull, but he eliminated the details that didn't matter and focused only on what mattered.
This is Picasso, this is Abstraction.