If there is one thing that can be guaranteed it is that anything that can be misused will be misused. That applies to sayings as much as to anything else. The thing, though, is that there are sayings that seem primarily to be misused, especially these days.
Take this Tamil sayings for example - 'Aindhil valayathadhu aimbadhil valayumaa?'. Literally, it connotes that what is not flexible at the age of 5 is unlikely to be flexible at the age of 50. Originally, it probably was meant to tell kids to learn as much as they can, develop mental and flexibility, while they were still young, because it would become more difficult to learn with age. It, also, probably was meant to excuse the old for not being able to learn newer things. But why would someone use it to ridicule or discourage any old person when (s)he is trying to learn something new? Yet, there are those who do it. This saying, though, has not yet achieved the exalted status of being primarily misused...yet!
And then there is this 'Money cannot buy happiness' thing. The purpose of that is to say that merely pursuing money will not lead to happiness. What sort of moronic brain would think that it also means that 'Lack of money does not cause unhappiness'? Yet, apparently, it is being increasingly used to tell the poor that they ought to be happy because they do not have money. I find it difficult to believe that most people genuinely think this way but what do I know? Human irrationality is unfathomable.
The one saying that apparently has reached the exalted heights of being primarily, even exclusively, misused seems to be 'Handicap is all in the mind' as applied to people who have a physical handicap.
A handicap obviously imposes limits. But, then, you do not need to have a physical handicap in order to be limited in the options you can pursue. If you emit sounds like the mating call of a male donkey every time you open your mouth in song, your chances of being the next Mohammed Rafi is, to put it mildly, close to Nil. If walking to the water cooler makes you hold your sides and pant for five minutes, Usain Bolt need not feel threatened by you. And, yet, you do not feel that you are fated not to succeed nor, indeed, do you think any the less of yourself for that.
Which, precisely, is the point. That a physical handicap may limit some possibilities but the concerned person should not let that get in the way of his success. It is to convey THAT that we use this saying - Handicap is all in the mind; AND to say that seeing such people as useless is a handicap in YOUR mind. But, nowadays, I believe that the tendency is to use it to mean that there is no real problem for them because they cannot see, or hear or whatever. It is all in their mind! Now THAT is an attitude which would qualify you as mentally deficient...in a more rational world.
The way things are going, I'll need to adopt the other saying. 'Speech is silver; silence is golden'. Till THAT one gets messed up, too!