They aren't all like this but to stick with the 40h vs. 80h framing, the 2x can make a difference.
1) Compounding. Assuming sustained productivity (this is usually unreasonable), it's not just you outputting 2x, it's a bunch of people cranking out 2x and your next up efforts compound on top of those initial boosted efforts.
2) Timing. Some startups are in positions where launching ~months before a competitor could tip the scales.
3) Hiring. It's very difficult to grow headcount at the exactly correct rate alongside business growth.
4) Fundraising. Growth rate is the top metric for raising additional funding.
1) Compounding. Assuming sustained productivity (this is usually unreasonable), it's not just you outputting 2x, it's a bunch of people cranking out 2x and your next up efforts compound on top of those initial boosted efforts.
2) Timing. Some startups are in positions where launching ~months before a competitor could tip the scales.
3) Hiring. It's very difficult to grow headcount at the exactly correct rate alongside business growth.
4) Fundraising. Growth rate is the top metric for raising additional funding.