It's really hard to be critical of your idea and to be super enthusiastic and passionate about that idea as well. In theory, this works but in practice it's super hard. I have tried it. Either I'll be super exuberant and tend towards over optimism or be super critical and get demotivated like you've mentioned.
I think allocating a specific time to poke holes in an idea might really work.
Another option that I have found helpful is external validation. You talk or demonstrate your ideas to outsiders and they are generally critical of your demonstration. This can be an eye opener some times. You as the idea originator, can then take a real hard look at the critical feedback and test out if that feedback really breaks the idea. There will be a ton of armchair criticism that you can ignore, but you get specific pointed criticism that is super helpful.
Even better is to have a co-founder or someone internal who can take a critical stab at your ideas. Of all the reasons that are out there for having a co-founder this might be the most useful one, especially for experienced folks. It is a bit tricky to make this kind of co-founding relationship blossom though.
I think allocating a specific time to poke holes in an idea might really work.
Another option that I have found helpful is external validation. You talk or demonstrate your ideas to outsiders and they are generally critical of your demonstration. This can be an eye opener some times. You as the idea originator, can then take a real hard look at the critical feedback and test out if that feedback really breaks the idea. There will be a ton of armchair criticism that you can ignore, but you get specific pointed criticism that is super helpful.
Even better is to have a co-founder or someone internal who can take a critical stab at your ideas. Of all the reasons that are out there for having a co-founder this might be the most useful one, especially for experienced folks. It is a bit tricky to make this kind of co-founding relationship blossom though.