Efforts to tackle the gender pay gap could be thwarted by the tendency for women to be pessimistic about their earning potential, research has suggested.
A study by the University of Bath found that women underestimate their earnings prospects, while men consistently overestimate theirs.
This leads to women having lower expectations and little inclination to push for higher wages or promotion, or seek a better paid position.
When men are dissatisfied they are more likely than women to try to engineer a pay rise or promotion, or change jobs in the pursuit of better pay.
The findings, published in the Journal of Economic Behaviour And Organisation, are based on analysis from the British Household Panel Survey.
Dr Chris Dawson, senior lecturer in business economics at the university's School of Management, said: "If low female expectations in terms of pay is fuelled by a pessimistic outlook, then even without discrimination and progression-related issues, women will continue to underestimate themselves and continue to inadvertently accept pay inequality.
"It has serious implications for policy that is trying to address the gender pay gap and suggests more needs to be done to actively advance women at work, without relying on them to self-select for promotion and senior opportunities.
"The takeaway message of this research is not about putting the responsibility on women, but recognising that without policy measures to address this, we run the risk of never closing the gender pay gap."
The researchers say the finding adds to the mix of causes of the gender pay gap - work, society and family - and questions whether policy measures will address the gap.
In 2016, the Office for National Statistics put the gender pay gap at 9.4% for full-time employees.
From April 2017, new gender pay gap regulations will require companies to publish information on the difference between male and female salaries.
Professor Veronica Hope Hailey, dean of the School of Management, added: "Whilst the role of unconscious bias in gender relations in the workplace has been well documented, this new research demonstrates the role of unconscious pessimism and passivity on the part of women.
"It shows the importance of people management practices that enable and encourage women to progress and recognise their value.
"The onus is on policy makers and employers to foster female talent so that initiatives to close the gender pay gap can succeed."