I'll put it another way. Most code isn't performance-critical. If you choose to write everything in, say, assembler, most of it will give you little or no gain.

I'll put it another way. Most code isn't performance-critical. If you choose to write everything in, say, assembler, most of it will give you little or no gain. Assembler's harder to write than Java, so every line is costing you money, whether it actually runs faster or not. The _effect_ is the same as speculatively optimising every line: substantial cost, uncertain benefit, potential to introduce bugs, etc etc.