I've met a few very accomplished (maybe not quite as accomplished as Bellard) people who are kind and not at all arrogant about it. I think a lack of arrogance and a generous view of those around you can really help someone to accomplish a lot.
Arrogance is generally a hindrance to learning. If you already know the "best" way to do something, your less likely to learn a better one. If someone shows you a better way of doing a thing, you're much more likely to take it as a challenge (someone is showing you that you don't know everything) and get defensive about it, instead of being receptive to improvement.
If you take a generous view of those around you, you're much more likely to be able to learn from them. If you are kind, people are much more likely to give you assistance. If you are willing to teach, you end up learning more, as having to explain things also forces you to clarify your own thoughts.
And it's not just a uni-directional relationship. The more secure you are in your own accomplishments, the less feel the emotional need to tear down others. The more you can honestly see that you've been helped in your intellectual endeavors (through advice, teaching, resources, etc.), the more you feel motivated to give back.
Being kind and humble isn't the only path to accomplishing great things, of course, but I've seen enough examples of it to conclude it's a very viable path. And it has the added benefit that if you don't quite make it to greatness (most of use won't), you won't have a whole bunch of people thinking that you're an egotistical jerk.