To Write or Not to Write?

Suspension of disbelief. Those words haunt me. I can't let them go. I want to save them for times when I can do nothing about it, not just lump anything that seems too much challenge into that category. Unfortunately, that does often slow down my storytelling. I know I should just go with the mantra: "write first, fix later."

However, I've found that details (especially involving science) can dramatically change a story: oops, it can't be done that way - shall I invoke the magical "suspension of disbelief" or research to find out how it can (maybe only improbably) be done?

So does one continue to write knowing details might significantly change the story, or just keep going?