Yes Boss: How to deter sycophancy in your team

In the 2006 Hollywood comedy-drama The Devil Wears Prada, the character of the notoriously domineering editor Miranda Priestly (played by the immensely talented Meryl Streep) is afforded a heightened sense of authority by the sycophancy of those around her, in particular Miranda's snarky assistant Emily Blunt (played by Emily Charlton) and the Runwaymagazine's creative director Nigel Kipling (played by the suave Stanley Tucci).
The character somehow obligates all the adulation, applause and approbation showered upon her by those around her, making her swollen head a little more, well, swollen. Both Emily and Nigel, as it happens in the movie, get close to Miranda (the power centre) before being unceremoniously ejected from their positions of responsibility because someone better suited for the job comes along (in the case of Emily) or a sacrificial lamb is needed to protect the leader (in the case of Nigel).
Flattery will get you nowhere, or so goes the adage. But a lot of people in a lot of workplaces across a lot of industries will tell you otherwise. That they've seen sycophants climb the hierarchical ladder several steps above their genuine calibre simply on the back of hokum. That those working hard but not succumbing to exalt their 'superiors' have not seen much growth in their careers. The point is that, unfortunately, you can't even begin to argue with such wisdom - it happens all the time. But that still doesn't make it right. At best, sycophancy is the worst thing to happen for teamwork, and at worst, can end up stalling a whole project or even organisation because it inhibits growth.
Flattery, sycophancy, cronyism. call it what you may, but it creates a toxic environment that discourages innovation and differences of opinion, leading to a stalemate in corporate growth. It may give a competitive advantage for personal growth of a few individuals, but it will accentuate a false sense of achievement and success, engendering a dysfunctional culture of unfair incentivising of the sycophant and demotivating the rest of the team members. Irrespective of the size of your team, as a team leader, it is your responsibility and, indeed, moral obligation to not take 'yes' for an answer.