Many years ago on HN, I think before he even became part of YC, Paul Buchheit said "You have to be arrogant enough to believe that everybody else is wrong, but humble enough to believe that you may be wrong too." That about sums it up.
This means that public response to the bare idea is never a good barometer, and you have to look to other things for data about whether it's going to be successful enough. This requires rigorous study and brutally honest introspection.
Don't get bent out of shape if people don't understand or respect what you're doing, but don't assume you're invincible or automatically right. Some wanna-be entrepreneurs waste their entire adult lives starting failing business after failing business, assuming that starting a business is the key to success, and that any idea they have is intrinsically valuable. Don't do this.
Statically, you're just as likely to be right with the first idea as the one you're sat on for months
In practice, that usually means do the minimum you can to verify the key assumptions of each idea, back out and try something different if any key assumption doesn't hold, and if you find something that has a good chance of working, stick with it.
If you sit on an idea for months, then that means it has survived a a good deal of reasonability testing and careful analysis, as you have been mentally prodding and poking the idea for a while, and haven't found a good reason to abandon it yet.
While the idea you just came up with has been through absolutely no deep analysis, by definition.
The subconscious mind is incredibly powerful, but it needs time to do its work.
Of course, slowly acquired self-delusion and emotional entanglement regarding the idea is a risk. But this varies significantly among people, can be somewhat defended against, and doesn't negate my main point.
I will say that doubters are everywhere and you do have to be able to persevere. My own wife was one of them with one of my companies. She'd say why are you spending so much time on that business when it doesn't make any money? I also met with an industry expert at the beginning and they told me not to bother; that there's already an 800 lb gorilla in the space and the market doesn't really need another entrant. Needless to say I bootstrapped it to 40k MRR and that gorilla offered to buy my company and I told them no.
Many times the doubt is not about your idea; people are just scared of any existing competition. They think - oh there are other companies doing that. Non-entrepreneurs seem to get more jazzed about new ideas that aren't being done and they get completely disappointed and paralyzed when they find out their idea isn't new and someone is already doing it. To the point they won't even see how they are doing it and see if they can do it better. I get jazzed when I see companies making a lot of money in a niche but not doing it well.
For many people, maintaining the ego on your idea/vision results in second mortgages on their house, high credit card debt, a lot of time away from family, and not knowing when to hang it up or change course.
Separately - taking the ego out of ideas is definitely a good thing when building a company with one or more partners.
Having ego in the idea means to equate the idea with yourself. So if someone criticizes the idea, ask questions, points out flaws, or issues with it a) don't take it personal and b) you need to be open to those and not dig your heels in refusing to adapt because "then it isn't my idea!"
You should stick with your vision, but not tie your ego into how you originally planned to execute towards that vision.