Short version: Taking advice is not an easy skill to master. I ought to listen to the advice itself rather than assume its validity based on the person offering it.
I have a bad habit when taking advice. I find it very difficult to listen when the advice comes from someone who does not follow that advice themselves. This is a sort of reverse authority bias, whereby I ignore good information that ought to be taken on it’s own merit. An intuitive example is the sporting one, a coach might study the tactics and strategy of a game, know their players and those of the opposition, the biomechanics of the body, and about nutrition and rehabilitation, and yet be themselves at a poor level of fitness. Thereby they might espouse accurate, useful, and ultimately critical advice, whilst being a terrible player themselves. Sport is also a good example of my bias at the group level, as often it takes skill in the activity to earn enough respect to be in a position to offer advice.
Further, I can find myself confronting the person giving me advice if I feel they are not being consistent to the underlying principle. This often comes across as confrontational, which is not how one should approach an offer of help (of which giving advice is a type). Even if it is not a direct confrontation, by challenging the person I distract myself away from considering the advice, and how it might address my own inadequacies. Seen from this perspective the motivation to react this way is obvious: it is much more comfortable to see someone elses weaknesses than our own. Conversely, once accepted and understood, it is only our own weaknesses that we are able to correct.
Confidence vs. Persistence
I am learning from the beginners rowing course, that while being confident is helpful (it prevents unnecessary hesitation, lowers stress, and makes the whole process more enjoyable), persistence (actual time practicing a skill, making it automatic) helps more.