Explanation:

- Telling someone something you admire about them is a random act of kindness. It requires little effort but offers great benefits.

- Many people go through life wishing for acknowledgment from others. Expectations are higher from family and friends.

- Even compliments from strangers are appreciated, but they need to be genuine.

Options Explained:

1. (so): Used to indicate a result or consequence. Not fitting here as it's not showing opposition or contrast.

2. (however): Indicates a contrast. Fits well as it contrasts expectations from family/friends with contentment from strangers.

3. (and): Adds similar information. Less appropriate as the sentence focuses on contrast.

4. (unless): Shows a condition. Not suitable since it's not conditional.