I agree with that person point on that not being a limiting factor. SciHub and all the networks of exchange of publications before that (I've seen exchange of proxy accounts and forums to do that since 2003, unsure about what existed before) have helped with that a lot.

Just to list a few points that come to mind:

Environment:

- A university that doesn't provide the ressources necessary (equipment, computing ressources with adequate expertise)

- Colleagues that are not supportive or worse putting you down for internal competition (just fame, attracting the most promising grad student of the year, or funding lines for grad students and postdocs)

- Intellectualy poor environment, colleagues that have no understanding and no willingness to understand your field of research

Money:

-Difficulty to compete when it takes you 80% of your budget to do 1/10 of a big lab (behind the name of a single person but really a group of 10s employees) can do with their large fundings. This is especially true of US vs many other countries.

Sociological:

- Gender (we know that women are not "allowed" to grow as much as men in some domains)

- University delivering a PhD, I still see people in their sixties being presented as a graduate from (pick an Ivy) and people ignored in discussions at a table of Ivy league graduates (despite that person being an expert)