What is the difference between きつい and 辛い（つらい）?

Question

They both have the same meaning of "hard, difficult, tough"

Can someone please explain the difference and give examples of when both are interchangeable and when it is not?

For example:

きつい仕事 or 辛い仕事

貧乏はきつい or 貧乏は辛い

etc.

What is the nuance in meaning?

Answer 1

In general

きつい implies difficulty, in the physical, logical, or opinionated realms

つらい implies difficulty in the emotional or interpersonal relationship realms

For the 仕事 example

仕事がつらい means that work is difficult to the point of physical and mental distress or pain.

On the other hand, 仕事がきつい means that work's definitely not easy, and some serious effort is required, but it still hasn't reached the threshold of "I can't do this anymore".

Reference

Examples of きつい

(based on https://dictionary.goo.ne.jp/jn/52804/meaning/m0u/)

1. Harsh sunlight or a strong scent can be きつい
2. The taste of something, or a food/drink can be きつい
3. The application of force can be きつい if it's too strong.
4. A garment that's too tight is きつい
5. A rule or request can be きつい
6. Work can be きつい if it's really difficult to do well.
7. Someone's personality can be きつい

See https://dictionary.goo.ne.jp/word/en/%E3%81%8D%E3%81%A4%E3%81%84/ for a bunch of English examples

Examples of つらい

(based on https://dictionary.goo.ne.jp/jn/148479/meaning/m0u/)

1. a person being "cold" to someone else is つらい
2. Work or practice is つらい if it's very mentally and physically taxing or stressful
3. something is つらい if it's problematic and difficult to deal with
4. someone is つらい if he/she is inconsiderate of another's feelings
5. someone is つらい if he/she is irritating

See https://dictionary.goo.ne.jp/word/en/%E8%BE%9B%E3%81%84/#je-50515 for a bunch of English examples (includes 辛い as からい as well)