Answer:
The sentence it will introduce will be contrasting to the sentence(s) before that.
Explanation:
E.g. I woke up late. <em>However</em>, I got to school on time.
["However" here contrasted the idea that "I" might be late for school since "I" woke up late]
There is no sentences stated here-
Answer: a lament for the things that the speaker lost.
Explanation: It's also a reflection on what wise people learn from their life experiences.