It's interesting to examine the claim of "individual errors".

An individual error is one that's completely out of character.

If "individual errors" are made repeatedly, it's <not> an individual error.

A team's players are a known resource. Each has their own characteristics. Good or bad, adequate or not. No-one is perfect. Basic competence is required - a minimum acceptable standard, both of personal motivation and technique. Players can train, but they are what they are

Teams are a different thing. Individual players have strengths and weakness, but a team can be structured to emphasise strengths, while either hiding or covering for the weakness of one player with the strength of another

If a player's weakness is repeatedly exposed, you can hardly blame a player whose weaknesses are known and worked on every day.
What's really being exposed is the failure of the team's structure to hide or compensate for a known weakness

This <can> be a failure in recruitment of basic competence into a team's available resources - when it comes at a price and has to arrive from competitors it's not always possible to bring it in during a limited window, but once a squad is fixed, it's then a failure of management

The concept of "individual errors" being to blame over the last 20 years became pronounced during AVB's tenure. No-one ever said it under Mourinho x2, Ancelotti or Conte. In the more recent Mourinho & Conte eras it was a failure of recruitment, never of management

One factor that's most interesting to recall under AVB was that Petr Cech had his worst performance as a goalkeeper in his whole career, both up to that point and up to his Chelsea departure. Oh, not entirely. Worst performance up to March 2012, when AVB was sacked. After that...

The other players producing "individual errors" (or inadequacies) in that season were John Terry, Frank Lampard and Didier Drogba. Are you fucking kidding me?
Not individual errors, failure of resource management by forcing players into their weaknesses, away from their strengths

Examples of top management of players of inadequate competence (at stage of career)
Mourinho2: Luiz incompetent at CB moved to DM. Matic in to replace permanently
Mourinho2: Rotation of Torres\\Ba\\Eto'o to make one good forward every game from 3 inadequate ones - 31 goals

Mourinho2: 2014/5 Terry, finished as a CB, surrounded by Azpi (LB) & Matic, played 38 games and won PL - masterclass
Mourinho2: Zouma, zero awareness around him at CB, given M2M marking job v Kane - all danger in front of him, won LCF

Conte: Incapable defenders in a 4, Luiz & Alonso recruited, shape change to hide Luiz behind Azpi & Cahill & hide Alonso & Moses' inadequate defensive ability at wingback to win 13 games conceding just 4 (6 in 16). Won PL at a canter

What we have now is 4 CBs, with plenty of individual shortcomings, exposed to their weaknesses through inadequate team structure.
A GK with known technical shortcomings, exposed even further (see Cech 2011/12) compounded by CB inadequacy & exposure

These are not (only) individual errors - every team has those. These are team management failures.
The mistake made by Thiago Silva in his first game - that <is> a genuine individual error <because> it's unusual. As with Mendy, the basic technical competence issue is covered.

Silva is already 36 and there's only 1 of him. His arrival can only be a stopgap. There <is> a recruitment issue, certainly - I wanted 3 CBs in this window - not arsed about attacking players, though you get them while you can.
When Silva leaves, team structure has to be solved

I'm happy with the concept of Lampard. I'm happy that Morris knows about team management in a novice environment with players that weren't always the best. But there are clear gaps.
I'm not happy that I have a perception of close-minded cliqueyness (if that's a word)

I'm not happy Newton, who carried RdM when the 2012 season was salvaged by the CL\\FAC double, was sidelined to the point of departure. While personally happy Luiz & Hazard were fucked off, I'm not happy it extends to the seemingly permanently sidelining of previous favourites

So, happy with the concept of the current management, much less happy about some of the practicalities, which include blindspots that appear on the pitch every single fucking week with little or no apparent correction.

Let's be honest with ourselves here. Because until we do, what we're seeing that we like is going to continue to be held back by what we see that we don't like. And don't think for one minute there won't be consequences that we also don't like. Because Roman is still Roman.