学”is "learn",“而不”and not,without,“则”will be,lead to,“罔”fruitless,labor lost,“思”think,“殆”danger,perilous.So,the whole sentence ,“学而不思则罔,思而不学则殆”,mean that leaning without thinking leads to confusion; thinking without learning ends in danger.that is,a good learner could not only learn knowledge but also think things and master it. 学”is "learn",“而不”and not,without,“则”will be,lead to,“罔”fruitless,labor lost,“思”think,“殆”danger,perilous.So,the whole sentence ,“学而不思则罔,思而不学则殆”,mean that leaning without thinking leads to confusion; thinking without learning ends in danger.that is,a good learner could not only learn knowledge but also think things and master it.