I largely agree to what you said, but I don't think that it's wrong for a Bitcoin investor to check the price chart most times, because by doing so he might sees an opportunity to buy aggressively if he has the reserve funds to do so, because he can't be aware of the dip if he is not aware of what's happening in the market, so it's not a bad thing to monitor the chart, what's bad is doing it in excess, because excess of everything is bad.
As for the aspect of being emotional that you spoke of, i don't think it's possible for someone that is only thinking long term and knows the real characteristics of Bitcoin that volatility is it nature, so he will know that it will definitely recovers no matter how dip it fell, it's only a newbie investors that knows little or nothing about Bitcoin will be emotional and sell in panic, not someone that knows all it takes to invest in Bitcoin and be successful.
Hey dude, the reason to stay off charts is because it might trigger investors to start having the mindset of withdrawing profit or even getting tensed because of the status of the market at the time being, there is more disadvantage attached to checking of price chart than the advantage, a long term investor has nothing to do with price chart so you know why, it is adviseable not to start what you can't finish, since we know the emotions thats attached to that chart, whats the need of doing something that can get you off the lane.
A good bitcoin investment strategist don't attach emotions when the price of bitcoin is dipping, infact he know that it is a good opportunity to buy on a lesser price so what he does at this time is to make sure he buys agreeivelly not because he wasnt buying before but because he don't know when the dip will resurface or last to, emotional sell are for traders and newbies but why we advise that long-term investors should stay away from charts is to avoid anything that can stand as a discouragement, you never can tell events can change individual mindset so it is better to stay focused you know what I mean.