If I was in your position and hypothetically maintained a...

If I was in your position and hypothetically maintained a positive long term outlook on this stock but was conscious of portfolio composition, I would take a third (or a quarter) of the profits and let the rest run without looking back. Be glad that you have locked in some of your profits, and don't regret it as you should see it as a trade off in terms of risk/reward. I did the same thing with ALU and sold a third at $15 (entry price $6) - psychologically I have no regrets as I followed my rule and was disciplined even though the price is now around $27.

Currently NEA is about 12% of my portfolio (of 20 stocks), my entry points were $1, $1.4, and $1.7
Hypothetically 1/2 of any portfolio would be above my risk appetite, diversification is key! Anything nearing 20-25% of my portfolio I would start taking rebalancing seriously, but instead of selling I would buy up on my other high conviction stocks to reduce the % of NEA.

If I felt all my other high conviction stocks were fully priced and I didn't want to enter, well that's a great problem to have!!
My view is that you should always have an exit price, or a price where you can take some of the profits and let the rest run - obviously this may change due to significant market announcements, but as an investor you will become much more disciplined in your approach.

Not personal advice of course... everyone is different and you should always seek unbiased professional advice if you're unsure!