How much is it going to affect one's career in the absence of a mentor?
The higher up I go in corporate life, the more that analogy holds.
The short answer, yes a mentor can be incredibly useful and if you find someone you admire by all means soak up their knowledge. But just looking for a mentor for the sake of it seems like an insecurity. I.e. There isn't someone out there with all the answers for you.
The good news is that you can and should have mentors any every point in your career. Most importantly, your mentor does not have to be your direct manager, and you can have more than one mentor, e.g. a mentor for technical work, a mentor for presentation skills, etc.
As my dad used tosay: the stupid don't learn from their mistakes, the smart learn from their mistakes,and the wise learn from other people's mistakes.
Their importance lies in the fact that they can guide you to and through a smaller set of right paths towards your goal bypassing the much much larger set of all wrong paths. They help short-circuit the learning ramp.
However if you develop a Auto-didactic mentality, you can do without a "full-time" Mentor; just receiving occasional advice is enough.
I would say it is like visiting a new city, you can spend hours researching the best landmarks, attractions, events, night life, read online reviews, etc... But will probably not be better than just going with a local guide or friend. Guides offer immediate insight, right answers to the wrong questions, might share local stories/curiosities on subject. Take you to the best places, actually local and interesting, instead of the same old touristy attraction traps. Curate the visit for the time, and interests, you have. Adapt the journey to unexpected events... You might make friends, most time better than being the lone warrior on the road to nowhere
They'll help you better guide your career. Avoid workplace traps.
Young/new people tend to focus to much on showing off. Wasting endless time fixing every small or tangent problem because they can. But with the insight of the bigger picture it is easier to focus and produce relevant work that moves the company, career, and knowledge forward
and esp. it's dwarfed by more needed a motivator instead of mentor need