Not every program will be able to take input in stdin and output to stdout. If you have a --file (or -f) option, you'd do well to support a "-" file argument, which means either stdin or stdout, depending if you're reading or writing to -f. But you won't support "-" if the -f option requires seeking backwards in a file. Neither will you be using stdin or stdout if binary is involved (because tty drivers).
'One thing well' is often intended to make people's lives easier on the console. Sometimes this means assuming sane defaults, and sometimes just a simpler program that does/assumes less. Take these two examples and tell me which you'd prefer to type:
Write concise technical documentation. Imagine it's your first day on a new job and you need to learn how all your new team's tools work; do you want to read every line of code they've written just to find out how it works, or do you want to read a couple pages of technical docs to understand in general how it works? (That's a rhetorical question)
Definitely provide a verbose mode. When your program doesn't work as expected, the user should be able to figure it out without spending hours debugging it.
'One thing well' is often intended to make people's lives easier on the console. Sometimes this means assuming sane defaults, and sometimes just a simpler program that does/assumes less. Take these two examples and tell me which you'd prefer to type:
Write concise technical documentation. Imagine it's your first day on a new job and you need to learn how all your new team's tools work; do you want to read every line of code they've written just to find out how it works, or do you want to read a couple pages of technical docs to understand in general how it works? (That's a rhetorical question)Definitely provide a verbose mode. When your program doesn't work as expected, the user should be able to figure it out without spending hours debugging it.