That makes sense. If you are flying out of Denver (high altitude) on a summer day, you need a TON of runway to get off the ground. There are some aircraft that

That makes sense. If you are flying out of Denver (high altitude) on a summer day, you need a TON of runway to get off the ground. There are some aircraft that simply can't take off fully loaded from high altitude with the runways that exist. The solution is to not take off fully loaded (lower the weight) So you either don't fully fuel up, or you remove cargo/passengers. It's very common, and by design. The software exists so that you know not to fully load the cargo bays if the conditions don't allow it (cargo makes airlines a lot of money).