wear thin

バングラデシュ首都ダッカの飲食店で起きた日本人７人全員が亡くなった人質事件。事件後のダッカは以前と少しも変わらないように見えて、どこか雰囲気が違うようです。記事はCNNからの引用です。
wear thinを辞書で調べると「〈衣服が〉すりへって薄くなる」とありました（『プログレッシブ英和中辞典』小学館）。ここでは「ショックを感じることが少なくなってきている」と解釈できます。（Koyamamoto）

Stunned residents after terror attack: 'Bangladesh was never like this'
Dhaka, Bangladesh (CNN)Except for the stern-faced police officers standing guard while a swarm of television journalists jostled for the best vantage points, Gulshan Road No. 79 looked no different this Sunday.
Cars blared their horns at rickshaws drifting into their path. Street peddlers scurried by, calling out the names of the fresh fruit nestled in baskets on their heads. Pedestrians hurled profanities at drivers as they dodged and weaved in between traffic.
If Dhaka is in mourning after its deadliest and boldest terrorist attack, it certain doesn't show it.
An optimist will call it resilience — a city buckled but unbowed.
A pessimist will call it resignation — a people so numb to the depressing regularity of attacks that the shock has worn thin.
But talk to some of the residents and they'll tell you that this time, it's a different emotion that overwhelms all others: Apprehension.
http://edition.cnn.com/2016/07/03/asia/bangladesh-terror-attack-reaction/index.html