The reason why investor can decide on the above questions is because they don't have strategy and plan.

The fundamental of the investment is very important. First criteria is u must satisfy yourself whether ur selection of your investment is a good and resilient one. Once u satisfy yourself with that, then it is very easy to decide. When the price is low, u keep entering to average down. U will not be able to identify the bottom but if u have a plan (like down by x% or x amount then u enter). Without a plan, u wont know when to enter.

This is why many investor exit the market last year and those who stay invested or even top up during down period get to reap off the benefits when it rebounded.

Back in 2008 when the market was bad, auntie A invest more when the investment is losing money. When comes to 2009, uncle B enjoys a 60% rebound but auntie A who invests more when the market was low enjoy 80% rebound. In this case, both auntie A and uncle B invest into the same investment, which is good and resilient, just that A top up when it's low and B didnt top up.

Not saying that history will repeat but if u know your investment well, have a plan / strategy, then u will succeed more than those investors who doesn't have the knowledge.

Also, those "sifu" is partially right bout average but this is half the story. Did they tell u the other half of the story is to satisfy yourself with a solid and resilient investment? If one keep average down a lousy investment, then this person is losing more money even more especially when the investment doesn't rebound or stay negative for the next 10 years or more.