Each startup pitch has its own strength and weaknesses. I would say one common mistake is to not have a good plan regarding timelines. For example, someone might be raising $1m for 12 months of runway. They want to land 5 contracts in that time and go out for a Series A. But if the product still needs 4 months of work to be usable, and then it takes 4 months to hire and train a sales rep, and then it takes 6-8 months to close a contract, then the math just doesn't work out. Whatever length of runway a company is aiming for, that needs to cover early product development + hiring sales + a typical sales cycle for your industry + time to do your next fundraising round (which can be 3-5 months).
Another mistake is to put off fundraising because you're "very close to landing a large paying customer." I've seen founders put off fundraising for a few months, then they realize the contract they've been waiting for is still going to take many more months of negotiation and diligence, but by then most investors have lost interest.
Leo, thanks for taking the time to answer my question. The first example you give makes perfect sense -- adding buffer time especially for easily overlooked things like training periods for new hires, etc. Great feedback.
We are preparing to hire a marketing role with enterprise sales experience, and it's a great reminder to lock in our sales strategy and build that into the timeline as we move forward for fundraising. Thanks for your help!