who is spreading strange advices like this? I read it all the time

what is better?

a)
you bought 1 BTC at $1.000
begins to fall, so you "lower average", 1 BTC at 800
continues to fall , so you "lower average", 1 BTC at 600
continues to fall , so you "lower average", 1 BTC at 400
continues to fall , so you "lower average", 1 BTC at 200
continues to fall , so you "lower average", 1 BTC at 100
you got 6 BTC for $700 avarege ($3100 total)

WORST CASE (never comes back): you lose over $3.000

b)
you bought 1 BTC at $1.000
begins to fall, so you sell 1 BTC at 800 (lost 200)
it falls below $100, comes back, and starts a trend on daily, you buy BTC 29 at $100 ($3100-200=$2900)

WORST CASE (never comes back): you lose $200