There must be a balance between
“The worker is worthy of his hire” (1 Corinthians 9, 1 Timothy 5)
“How will they hear if no one goes, how will they go if no one sends” (Romans 10).
The idea of Tentmaking (and, to some degree, BAM) is in part that funding issues are resolved in the harvest. The idea of long-term deployment is that funding issues are resolved in the sending church. No answer is a silver bullet. This is part of where the entrepreneurial nature of the missionary comes into play – the same kind of entrepreneurial spirit that is found in a startup.
When you read literature about pioneering business startups, you find that the area the founder spends most of his/her time in is finding (1) funds, (2) co-founders, (3) staff. Some funding models call for investors; others call for sales (make the product, ship the product, live off the revenue). There’s a lot of discussion about which funding model works best, but as with missions, there is no silver bullet.
Funding the ministry (as in funding business startups) takes hard work. Many startups fail because they do not successfully navigate this. We can expect some missions (many? most?) to fail [to be sustained long-term] because they do not successfully navigate it, either.
If you fail, try, try again.