Hoarding what you know makes you necessary for a month. Teaching it makes you respected for life.

Being the only person who knows how something works feels like security, and it is a short lease. Knowledge that lives in one head gets routed around eventually, and people resent the bottleneck while they do it. Giving it away costs you that edge and buys something more durable. Nobody forgets who made them competent.

Write down the thing you know that nobody else on your team does. Then show one person how to do it properly, not just well enough. You lose the feeling of being indispensable and gain the person who vouches for you later.