Computers have reached a point where even "slow" languages run fast enough to make the difference in speed irrelevant in many cases. We have the luxury now of sacrificing some potential performance to use a language that offers better first-class features and more powerful abstractions, which is important because it lets us get more code out the door in the same amount of time. On average, ten working but not-quite-optimized apps will do more total good than two working and really fast ones.
If I can write a Python web app in two weeks that would have taken me three months to write in C, those 10 weeks I didn't spend are a huge win. Now I can use them to do something else.
Most programs aren't performance-critical. As long as the code is reasonably written, most people won't notice the difference between something written in Python and some optimized code in C++. If you're having performance problems and need to speed something up, the biggest gains will come from improving your data model or moving your code into a better complexity class. Only in rare cases, like search services or high-frequency trading, will removing the relatively small penalties from things like language speed actually be worth the cost.
Make it quickly, make it great, make it fast enough to use, and ship it. Anything past that is rarely a good use of your time.
Reference: https://www.quora.com/If-C-and-C++-give-the-best-performance-why-do-we-still-code-in-other-languages
