pickthis: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/share/doc/mh-book/examples/mh/bin/pickthis - from package: mh-book

You may install the required package with command apt-get install {package}

Error in other languages:
pickthis: bevel nie gevind nie
pickthis: comandă negăsită
pickthis: comando não encontrado
pickthis: commande introuvable
pickthis: command not found
pickthis: käsku ei ole
pickthis: không tìm thấy lệnh
pickthis: komanda nerasta
pickthis: Kommando nicht gefunden.
pickthis: kommandot finns inte
pickthis: komut yok
pickthis: nie znaleziono polecenia
pickthis: níor aimsíodh an t-ordú
pickthis: no se encontró la orden
pickthis: no s'ha trobat l'ordre
pickthis: opdracht niet gevonden
pickthis: parancs nem található
pickthis: perintah tidak ditemukan
pickthis: príkaz nenájdený
pickthis: příkaz nenalezen
pickthis: команда не найдена
pickthis: командата не е открита
pickthis: 命令找不到
pickthis: コマンドが見つかりません