How good can one get at economics without formal training?

Is it possible to achieve solid understanding of economics by reading blogs and YouTube videos?

Or is formal training required?

If so, what kind of formal training? Would it be enough to study actual textbooks on those areas of economics one is interested in, or you need to go to some sort of school?

What do you recommend to amateurs interested in economics, how can they deepen their understanding, if they aren't planning to enroll in actual Economics degree at college / university?