Spot limit order - why spot price should be above limit price for selling?

https://academy.binance.com/en/articles/what-is-a-stop-limit-order ... "In truth, it will be safer for you to set the stop worth (trigger worth) a bit larger than the restrict worth for sell orders. "

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An instance. Let's say that a worth is 100 now. I'd like to pick 90 for spot worth in order that when worth was 90 earlier than, my order would have gone to orders ebook, now i hope that worth for selling might be 110. If worth after 100 doesn't go up, but falls down, i would like that crypto is bought at worth 90.

Why should i choose spot worth above restrict worth as a result of spot worth maybe gained't be reached? Spot worth ought to be the lowest selling worth where my order goes to order e-book and restrict worth the very best promoting worth.