Undergrad thesis advisor declined my LOR request...what do I do?

[HappyCat13]

At this point its kind of tough.

When you need something done, don't apologize and don't give anybody an out. Imagine if your boss called you on your day off and said "this is important, I need you to come in to work right now." You would probably be more likely to go in than if he said "I know you're probably really busy, but it would be great if you could come it to work today. I understand if you can't make it." Certainly don't thank him for not helping you...

You might email him back and tell him that you weren't able to find 3 other letter writers and you really need him to write you a (strong) letter outlining your research ability and that he is in the best position to do this. Also, let him know how important it is to you.

Good luck.

I agree with Deckard that your letter is kind of overly apolegetic. It's correct to write polite letters to prof. But don't be too polite to the point that it makes it very lengthy and couldn't convey what you want in a straightforward way.

Also, putting "if you can't write I would also understand" makes people think that "my letter might not be very essential and important" or "you already have backups".

When you really want something, phrase the urgency and importance in your emails. I start to learn this when my polite emails get no responses from one of my letter writers who is a very busy person. And my emails with short and instructive sentences get quick responses and immediate actions from him, such as title with "urgent reminder", and letter contents with "please submit this blah blah blah" or "without your letter my application would become incomplete after the deadline...".

You have worked for a few years. So I think you should know this email writing rule from your corporate environments. In my company I was trained that a overly polite and lengthy email would get urgent matters delayed.