What is equivalent of Indian saying "pottakkannente Maaveleru" means while actually the blind man is throwing stones in a waterless well (a job in vain), but he thinks he is throw stones at mango tree (where he will get mangos in return. mangoes are suppose to be valuable)
A expat community (from India) in a foreign country (say USA) is discussing about their home country rate (USD vs Indian Rupees) exchange rate). Everyone says the current exchange rate will remain the same (not exactly beneficial to the expat community). A person among them predicts that by end of the month the rate will increase (he does not have any proof or rationale) and so what he means is the expat community can get a better rate and end up earning better deal than today. One another skeptic amongst them say "pottakkannente Maaveleru" which in this context mean he is shooting in the air (same as stoning in a waterless well - no result) and that the rate will not improve (not benefit the expats).
Now according to the skeptic, but like a blind man the predictor's see himself stoning at the mango tree (which means predictor thinks his prediction will be true). The skeptic indirectly means that the predictor does not have any basis to say what he is predicting.
Importantly the general meaning is that
if his prediction comes true it is a fluke and if not than like any politician he will vanish into obscurity when the day comes.