"From the bottom of my heart"

Why do people say that?


Usually the bottom part of a jar isn't the greatest and no wants the smashed up jam or the week-old milk with the dried up milk crisps floating on top. If my heart was an ocean and I dropped stones with all my problems and guilt written on them, where would all those stones go? To the bottom of course. So when people make speeches to thank loved ones and other significant people with a slice of 'from the bottom of my heart', how is that actually thanking them? It only makes sense to say 'from the top of my heart' because you'd want to give them the best and realest part of your heart.