Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: What is the reason that playing games sometimes take on a more serious tone?
competitiveness
Various factors such as complex storylines, high stakes, or emotional engagement can cause games to take on a more serious tone.