Here are some things I've come to believe over the years...
Stop designing for yourself. Understanding what your users need and communicating that around the organisation is super important.
However research doesn’t tell you what to do, so don’t rely on it too heavily. Otherwise you can get stuck down rabbit holes and paralysis sets in. So focus on getting just enough research to inform decision making.
(By the way, I'm aware that “user” is a contentious term, so have mostly used it here for the sake of brevity. Feel free to substitute it with whatever term you feel most comfortable with.)
This is one of the benefits of the agile process.
However if you break things down too much, you lose the big picture view and entropy sets in. As such, you need to think both big and small.
However we can also spent a lot of time over analysing problems that are intellectually unanswerable, so other times it’s better to think by making and learn by shipping.
Knowing which approach to take when is tricky, and most people tend to default to one or the other.
However designers often take this for granted and get frustrated when business people who have been extremely successful without worrying about design, don't immediately drink the cool aid.
The most effective designers become advocates for design, form alliances, and pick their battles sensibly. However they also realise it's impossible to change hearts and minds overnight, so are in it for the long haul.
However it's bloody hard to do. Especially if you feel unsupported and marginalised by your company.
They set the standards others follow, act as coaches and role models to juniors, while having the trust and ability to influence business stakeholders.
However leads are all to often hired into management positions, and get sucked into an endless round of recruitment, budgeting, and planning meetings. They stop being effective role models, the team atrophies and attrition and dissension starts to rise.
However when your right thing gets blocked by somebody else's right thing, you almost always end up writing that person off as difficult or ignorant.
Rather than trying to convince the other person of your opinion, it's better to understand their opinion, get agreement on the problem you're trying to solve, and find a middle path.
This is one of the reasons why working with people is hard, why decisions take so long, and why the results are often mediocre.
As designers we often get stuck down rabbit holes that nobody actually cares about, and end up producing a beautifully designed and engineered product that nobody wants.
As such, more of the money you were going to spend on marketing should be diverted into design.
In short, marketing should support product. Not the other way around.
Much as I believe this to be true, history is littered with the corpses of well-designed products that failed to capture the attention of the market, while there are plenty of crappy products out there that have gained huge success because of superior marketing.
You have all the responsibility but none of the power. Everybody thinks they know better than you. It's impossible to satisfy everybody. When things go well somebody else will get the credit. When things go wrong, you’ll get the blame (even if you flagged it up from the start).
Everybody sitting around the table has a picture in their heads of what they want. They think its the same picture that the person sitting next to them have, but it's not.
The ability to visualise thoughts, beliefs, concepts and decisions is a super power. It gets everybody on the same page, or at least highlights where things unexpectedly diverge. It also prevents people from hiding behind ambiguity.