I pitched many, many times (and was often the lead on product sales), so I have a lot of experience with rejection. I agree with what others have said about learning and improving, so no need to repeat that.Here are some other things to consider.
Investors are not always right and or professional. So, if it seems like you're getting a load of ****, that isn't necessarily your fault. Specifics at http://robertvbinder.com/vcs-say-the-darndest-things/
Some people are more immune to rejection than others. Changing your mindset and attitude can help, but what works for me or the authors of how-to-sell and pop psychology books might not work for you. I tried some of that and it sometimes helped, but didn't prevent the sting. I came to view that disappointment as simply part of the game, in the same way that injuries are part of contact sports.
And being too tough-minded isn't a good thing either - looking back, I persisted long past the point of diminishing returns.
Hope this helps.