The timing of the sales was predetermined under what is known as a 10b5-1 plan, named after an SEC regulation that allows company insiders to avoid insider trading charges by setting up a schedule of sales in advance (typically a year).
I only know because I drove a CEO for the company I worked for to a meeting and we got to talking about stocks. He explained this loophole to me as his way to effectively trade how he wants with legal protection from insider trading.
"After Rule 10b5-1 was enacted, the SEC staff publicly took the position that canceling a planned trade made under the safe harbor does not constitute insider trading, even if the person was aware of the inside information when canceling the trade. The SEC stated that, despite the fact that 10b5-1(c) requires trades to be irrevocable, there can be no liability for insider trading under Rule 10b-5 without an actual securities transaction, based on the U.S. Supreme Court's holding in Blue Chip Stamps v. Manor Drug Stores, 421 U.S. 723 (1975)." 
The idea being the thing to maybe pay attention to are buys, not sells from those folks.
I worked at a place once where at a meeting the CEO was asked about selling a bunch of stock. He was pretty honest and said something like:
"I love this company and I'd love to 'double down' on it but as a private person most of my assets are in this company and it's time to diversify, even if just for my kids."
Anyway that was received well by most folks there.
The CFO noted "Not me I'm all in!".
Epilogue, the CEO was smart, the CFO less so... (granted CFO still did alright)
Capital loss is tricky because of wash salrs rules, so likely you won't be able to write off...
Typically shares are withheld to pay the tax before you ever see them. I.e. if your tax rate is 50% and you're getting an award of 100 shares, you'll only receive 50 shares in your account.
After that the shares are treated as if you'd purchased them at market rate. If you sell them immediately, there's no capital gain and no further tax to pay.
It's often possible to choose between doing that or keeping all the shares and paying the tax liability out of your salary.
By taper relief I mean you sell older shares first and get taxed on long term capital gains first in first out.
Zuckerberg sold $400 million worth in the last month. I think that's more news worthy.
(Zuck's funding his foundation, incidentally, and has been for years. https://www.vox.com/2018/2/14/17012846/mark-zuckerberg-faceb...)
If only the timing is predetermined then it defeats quite a bit of the purpose. Basically the idea is that the person cannot interfere with anything once the plan is set and thus cannot be accused of insider trading.
[edit--he sold all!]
He got 560,000, sold 265,160 and 294,840 was withheld to "satisfy tax-withholding requirements for the vesting of the restricted stock units".
If you own shares in a company with different purchase dates you can designate which ones you are selling. There can be tax reasons to choose one batch or another.
Sorry if it wasn't clear I must remember to write for ESL NH users.
> You can't sell shares you got ten years ago and not the ones you got yesterday.
What do you mean?
> The timing of the sales was predetermined under what is known as a 10b5-1 plan, named after an SEC regulation that allows company insiders to avoid insider trading charges by setting up a schedule of sales in advance (typically a year).
A big pile of stock is worthless if you can't sell it. Cook probably wants to diversify, buy a house, boat, fancy car, and whatever else rich people like to do with their money.
1. Is there any evidence that these insiders are good at market timing?
2. It would be illegal, risky and stupid for the CEO of one of the biggest companies in the world to dump stock on obvious insider knowledge. Do you really believe Tim Cooke is going to stake his entire coproate reputation for another few million bucks when he's already filthy rich? Maybe, but I'm skeptical.