Flexible means not stubborn.
How is the important team attribute of flexibility identified? The easiest way is to see whether someone is stubborn. Great teams have a lot of opportunities to measure stubbornness and flexibility because they have great feedback loops. If someone refuses to budge when confronted with solid feedback, they are not flexible. No adjustment is needed because they don’t think they are wrong. In fact, the stubborn teammate may even think the rest of the team needs to adjust while they stand their ground. This is obviously a problem for any team dynamic and must be resolved before any team can hope to move forward.