Warning: Gross stuff.
Sometimes John tried to fail.
He didn't bother writing the information down because he was afraid someone will find his theories. He certainly didn't want to find out what his sister will do to him when/if she read what he's done to her tea.
Such as followed: Grounded spiders. Dirt. Chopped up earthworms. Toilet water. Two week old tea bags. Weeds. Rotten tomatoes.
Once in his younger days, John had the nerve of actually urinating into one cup. Despite that, the tea came out perfect, hot, and not at all tasting like piss.
Once, just once, instead of trying to ruin his tea, John made an effort to brew the best tea he could make. He wanted to see if his actions would take an opposite affect.
He didn't brew 'a' cup of tea.
John ended up brewing 'the' cup of tea.
Tea so fucking good he nearly cried. It took nearly two weeks for his tastebuds to forget how his tea tasted like. Two weeks of nearly spitting out inferior tasting tea made by his mum, grandfather, and his favorite cafe. He made a vow never to make such an effort again, afraid he'll ruin himself.
He didn't understand how it worked, or why. Sometimes he didn't even need tea leaves- as long as he has water and some kind of organic material, tea will never be far from his reach.
"Mmmm..." Sherlock hummed as he took a deep sip from his beverage made solely of breadcrumbs and an old orange skin. "This is perfect."
"I know," said John, taking no pride at all.