A lot of the problems have come from managers simply making the incorrect decisions and repeating these decisions and hoping for different outcomes.
Martinez with his defending, set-pieces and having absolutely zero plan B even when we got worked out. Didnt we have our worst home record including 93/94 and 97/98 in his last season? He also insisted on playing Tim Howard who I recall was directly at fault for about 20 goals that season that a League One keeper would have stopped.
Koeman was a self-serving imbecile. He bought players at "their peak" but forgot to buy quality players at their peak. He was sacked for buying Cuco, Klassan, Williams, Bolasie, Vlasic, etc etc etc for absolute extortionate fees and not replacing Lukaku. He also presided over the sale of Stones, Barkley, Deulofeu and Lukaku who would probably still be the spine of our team now.
Allardyce was non-football men absolutely panicking. We stumbled and laboured to 8th under Fat Sam playing the worst football I have ever seen. A quality appointment would have got us to Europe easily. Relegation was never a threat.
Silva was a combination of all of the above. Bottom line though, when you continually pick Walcott, Schnedierlin and DCL when they are performing like League Two players, when you cant defend set-pieces and you go into the season without a centre-half or striker improvement then you will struggle. The injuries got the the sack (early) but that has been a godsend because we have now got Ancelotti. Silva's squad under Carlo will come close to Europe this season and would have broke the top 6 without those injuried to JP and Gomes.
Relax blues, it will all come good. We now have a manager who will instill leadership, organisation and trust from the fans.