What works best: Co-founder vs Collaborative vs Solo side projects?

Linked below is an interesting thread on r/startups with a question on the effectiveness or viability of collaboratively building a side project until it becomes successful.

Most Indie Hackers appear to have a full-time job and entrepreneurship is a side project done solo. Going solo is hard for lots of reasons:

• Many hats to wear / skills to be good at
• Hard to stay accountable/motivated
• Sets you up for 'bus factor'
• Available time can fluctuate drastically

Would building side projects collaboratively be easier than going solo?

What about solo vs having a co-founder?

https://www.reddit.com/r/startups/comments/8429i7/why_isnt_there_a_place_to_build_projects_together/
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IMO it's a great concept, but building a virtual team that can work together really well sounds very hard and the execution of the contributions/rewards system is probably very tough to get right.