a query on the adverb 'ALSO'

Dear friends



Would anyone be so kind as to enlighten me on my query on the use of the adverb ‘also.’



I used to have the notion that the adverb ‘also’ is used to talk about two ideas which share a similar quality. Hence, I used to produce sentences such as:



1. My sister is a wonderful housewife. She can clean, iron, cook delicious food; she can also take great care of her husband and kids.

2. My boss is not only a bad-tempered person, he is also notoriously stingy.



However, recently, I came across sentences like the following:



3. Although life in the countryside is very peaceful, it can also be lonely.

4. While a 5-day week allows office workers an extra day to rest, it can also turn out to be a tiring week if people spend that extra day going to parties instead.



So, have I been wrong in my previous assumption?



Thanks

donna