Yes, definitely good advice to buy the longest and widest-aperture lens you can afford, but we’re talking about lenses that cost £30K or more, and even hiring one for a 2 week safari costs a great deal.
Learning how to approach subjects is fundamental to wildlife photography, as is developing a full knowledge of the creature’s habitat requirements, seasonality and behaviour.
I’d pay less importance on “knowing when to walk away from a lousy photograph”, in much the same way that I pay little attention to waiting for the “perfect light”. Very often I’ve found that my best photographs have been taken in far from ideal conditions. Patience can bring great rewards.