at some point in your life you will be boiling fruit, water, sugar, and lemon juice in a pot to make a syrup or jam. the instructions will tell you to simmer for a certain amt of time. your timer will go off and you will look at the pot and go, "hm, this doesn't look thick enough. maybe i'll let it go for another 10 minutes." this is the devil speaking. it's only so liquid right now because it is at boiling point. it will thicken when it cools down. learn from the follies of my youth and do not let this happen to you

at some point in your life you will be making a sauce or a stew in which you need to add cornstarch to thicken it. and you will prepare a slurry of starch in cold water and think "this looks like way too little starch to thicken this amount of liquid." this is the devil speaking. cornstarch instantly polymerizes at 95°C and if you add too much it will turn into an impossibly thick goop.

at some point in your life you will be making some sort of cream based dessert that requires gelatin to thicken it. and you will soak some gelatin sheets in water and think "this is too few gelatin sheets for this amount of cream." this is the devil speaking. it will thicken in the fridge and if you add too much you will end up with milk jelly