I've been through deals with large financial institutions that have taken 2-3 years from an initial incredibly positive demo and PoC and strong buying signals, through to a signed contract.
IMO going through that successfully is also sending a signal that you have sufficient endurance - there's a large risk for a corporate to sign up for a long contract with a startup, they don't know how long you're going to be in business for. If the startup doesn't have the appetite to spend 2-3 years to get a contract over the line, then they aren't going to be a stable partner for the long term.
You need to also have sufficient numbers of small/medium scale deals so you're not 100% relying on elephant hunting.
IMO going through that successfully is also sending a signal that you have sufficient endurance - there's a large risk for a corporate to sign up for a long contract with a startup, they don't know how long you're going to be in business for. If the startup doesn't have the appetite to spend 2-3 years to get a contract over the line, then they aren't going to be a stable partner for the long term.
You need to also have sufficient numbers of small/medium scale deals so you're not 100% relying on elephant hunting.